Method for repairing a piston and shaft assembly

ABSTRACT

A method of repairing an end-of-car cushioning device for railroad cars is disclosed. The cushioning device is of the type having a piston and a shaft connected to the piston. In such devices, the shaft may become damaged with wear. In the disclosed method of repair, the old piston and shaft are removed from the cushioning device. The old shaft is substantially removed from the piston. The piston&#39;s true center is found, and a bore is cut through it. The bore is threaded, and an angled chamfer is cut in one end of the bore. A new shaft is provided with a threaded portion, the threads being adapted to mate with the threads of the bore. The shaft also has an angled chamfer adapted to mate with the bore&#39;s chamfer. The new shaft is connected to the old piston so that the threads engage and the chamfers abut.

BACKGROUND OF THE INVENTION

This invention relates to a method of repairing end-of-car hydrauliccushioning devices used on railroad cars. More particularly, the presentinvention is directed to replacing broken or cracked shafts used in suchcushioning devices.

End-of-car hydraulic cushioning devices have been used on freight andpassenger railroad cars to dampen train action buff and draft forces.Such cushioning devices are known in the art, as represented by U.S.Pat. Nos. 3,589,527 and 3,752,329. The cushioning devices disclosed inthese patents, as well as other cushioning devices in use today, utilizea one-piece piston and shaft arrangement to transfer outside couplingforces through a hydraulic fluid-filled housing. As the piston and shaftmove through the housing, they displace hydraulic fluid. The fluid ismetered through valves and other orifices in the housing to absorbenergy.

Each end-of-car hydraulic cushioning device is designed to fit in acenter sill pocket at an end of the railroad car. The shaft includes anend normally provided with a spherical bearing which connects to the carbody. The housing is connected to the coupler and is slideable withinthe sill pocket. The housing has metal stops which engage similarlimiting stops fixed on the inside of the sill. These engaging stopslimit the length of travel of the housing relative to the piston andshaft as buff and draft forces act upon the railroad car coupler,extending and compressing the cushioning device in its center sillpocket location.

Examination and testing of used cushioning devices and center sillpockets have shown that wear experienced in the pockets may impair thefunctioning of the limit stops. With such wear, as outside buff anddraft forces act upon the shaft and piston, the piston will contactother internal parts of the cushioning device, resulting in stress atthe connection of the piston and shaft, and at the connection of theshaft and spherical bearing. Depending on the load, the shaft may crackat either connection, eventually leading to complete failure of thedevice. Where these connections are achieved through heat shrinking orwelding, the shaft and piston or bearing may separate, further damagingother internal critical metering features, so that the cushioning deviceis virtually irreparable.

SUMMARY OF THE INVENTION

When shaft failures occur within an end-of-car hydraulic cushioningdevice, which uses a one-piece, friction welded, heat shrink welded orother similar connection between the shaft and piston, the failuregenerally occurs to the shaft, which cannot be reused. The originalpiston can, however, usually be reused with a replacement shaft. If theoriginal piston is reuseable, the method of the present invention may beused to repair the device.

To repair the end-of-car hydraulic cushioning device, the old piston andshaft are removed from the device. The old shaft is then removed fromthe piston. The piston's true center is found, and a bore is cut throughthe true center. Threads are then cut in the bore, and an angled chamferis cut at one end of the bore. A new shaft is provided, the new shafthaving a threaded portion at a predetermined position along its length.The threads are adapted to mate with the threads of the bore. The newshaft also has an angled chamfer at one end of its threaded portion, thechamfer being adapted to mate with the chamfer of the bore. The newshaft is then connected to the piston by screwing the threaded sectionstogether. To ensure a strong connection, a thread lock adhesive may beused in this connection. The new shaft is assembled into a housing andconnected to a spherical bearing, and the repaired assembly may bereused for cushioning of railroad car couplers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, in partial cross section, of a typical prior artpiston, shaft and bearing assembly used in end-of-car hydrauliccushioning devices.

FIG. 2 is a side view of a damaged prior art assembly.

FIG. 3 is an end view of the piston after the damaged shaft has beenremoved.

FIG. 4 is an end view of the piston of FIG. 3 after some of the repairsteps have been completed.

FIG. 5 is a side view of a new shaft.

FIG. 6 is an enlarged partial side view, in cross section, of a repairedpiston and shaft.

FIG. 7 is a side view of another type of prior art piston, shaft, andbearing assembly.

FIG. 8 is a side view, in cross section, of a repaired piston and shaft,of the type shown in FIG. 7.

FIG. 9 is an enlarged partial side view, in cross section of the pistonand shaft of FIG. 8.

FIG. 10 is a graphic illustration of a tension test performed on therepaired assembly of FIG. 6.

FIG. 11 is a graphic illustration of a tension test performed on therepaired assembly of FIGS. 8 and 9.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

In the accompanying drawings there is illustrated a piston and shaftassembly for use in an end-of-car hydraulic cushioning device for use onrailroad cars. Also illustrated is a damaged piston-shaft assembly, suchas would occur after the cushioning device has worn. As provided by themethod of the present invention, this damaged shaft may be removed andreplaced with a new shaft. When subjected to tension tests, the repairedpiston and shaft assemblies exhibit sufficient strength to withstandtensile loads of 900 klbs. (900,000 pounds-force) without disengagementof the piston and shaft.

Referring to FIG. 1, a typical prior art piston 10, shaft 12 andspherical bearing 14 assembly is shown. This assembly fits within anend-of-car hydraulic cushioning device, such as that described in U.S.Pat. No. 3,589,527 to Seay, et al., the disclosure of which isincorporated by reference herein.

In this embodiment, the piston 10 and bearing 14 are disposed atopposite ends of the shaft 12. Another typical prior art assembly isillustrated in FIG. 7. This assembly also includes a piston 10a, shaft12a, and spherical bearing 14a. However, in this embodiment, the piston10a is disposed along the length of the shaft 12a, rather than at anend. Such an assembly fits within an end-of-car hydraulic cushioningunit such as that disclosed in U.S. Pat. No. 3,752,329 to Seay, et al.,the disclosure of which is incorporated by reference herein.

In both of these typical prior art assemblies, the pistons 10, 10a, areusually welded to the shafts 12, 12a, such as by inertial frictionwelding or heat shrink welding. As the hydraulic cushioning devicewears, stresses act upon the connections between the shafts 12, 12a andthe pistons 10, 10a and the bearings 14, 14a. These stresses may resultin failure of the shaft, such as, for example, a break 16 in the shaftat the connection with the spherical bearing, as shown in FIG. 2. Itshould be understood that these stresses may cause breaks and crackselsewhere along the length of the shaft, such as at the connection withthe piston.

When such a break or crack occurs, it is necessary to replace or repairthe assembly or the entire cushioning device. By the method of thepresent invention, the piston-shaft bearing assembly may be effectivelyrepaired and then replaced in the cushioning device.

To practice the method of the present invention, the piston 10 and shaft12 assembly must first be removed from the cushioning device. The lengthof the old shaft 12 is then substantially removed from the piston 10, asby cutting along line 18 of FIG. 2. The piston 10 is positioned in alathe or other fixture designed to determine the true center 19 of thepiston 10. After the true center 19 has been determined, a bore 20 iscut in the piston at its true center through its axial length. Thisboring removes any remaining shaft material.

As shown in FIG. 4, threads 22 are then cut into the wall so the bore20, by, for example, single pointing, to a predetermined number ofthreads per inch and thread class. In the illustrated embodiment, a3.305 inch diameter bore and eight threads per inch, thread class 3 orbetter are provided. A chamfer 24 is also cut at one end of the bore 20,preferably on the outside face 26 of the piston. In the illustratedembodiment, a 1/8 inch chamfer is cut at a 45° angle.

As shown in FIG. 5, a new shaft 30 is provided. The new shaft has afirst threaded end 32, adapted for connection to the spherical bearing14. At the opposite end 34, the shaft is adapted to mate with thechamfer 24 and threads 20 of the piston 10. Accordingly, in theillustrated embodiment, this end 34 of the new shaft 30 has a 1/8 inch,45° chamfer 36 and a threaded portion 37, threaded at eight threads perinch. Integral with the chamfer 36, an enlarged diameter stop 38 isprovided. The diameter of the stop 38 is greater than that of the bore20; in the illustrated embodiment, the diameter of the stop 38 is 3.500inches. The diameter of the central length 40 of the new shaft is lessthan that of the bore 20, so that the piston 10 may be slipped onto theshaft from the first threaded end 32.

As seen in FIG. 5, the stop 38 is positioned such that chamfer 36, whichengages chamfer 24 of piston 10, physically limits further movement ofpiston 10 along shaft 12 in a direction away from threaded end 32. Thus,the stop 38 positions the piston 10 relative to spherical bearing 14 andalso bears a portion of the force when the shaft is exposed to draft ortensile loads. It is contemplated that such loads are more severe thanbuff or compressive loads. In this latter load condition, the threadedconnection between the piston and shaft transmit the force loads.

Providing a new shaft for an existing piston makes possible anotherimprovement. The shaft can be made from 1/2 inch to three inches longerthan the original shaft. This permits greater tolerance to wear withinthe sill pocket and reduces the possibility that a piston will "bottomout" within its cylinder in the cushioning device. This reduces thecause of shaft failures by reducing the possibility of associated impactforces upon the piston and shaft.

In the method of the present invention, the new shaft 30 is connected tothe piston 10. As indicated, the piston is slipped onto the firstthreaded end 32 of the shaft through the bore 20, slid along the lengthof the shaft, and then screwed onto the threaded portion 37 of the newshaft. When so connected, the mating chamfers 24, 36 abut each other, asshown in FIG. 6. In the connection between the piston and the new shaft,a thread lock adhesive should be used. An acceptable thread lockadhesive is "Loctite 271", manufactured by the Loctite Corporation ofNewington, Conn. The first threaded end 32 of the new shaft may then beconnected to the spherical bearing 14 and the repaired assembly replacedin the cushioning devices.

Referring now to FIGS. 7-9, the method of the present invention may alsobe successfully employed in repairing piston-shaft combinations of thetype where the piston 10a is disposed along the length of the shaft 12a.In this embodiment, as shown in FIGS. 8 and 9, the new shaft 30a has athreaded portion 37a and has a 45° chamfer 36a and stop 38a along itscentral length 40a. The stop 38a is located at a predetermined distancealong shaft 30a to position piston 10a with respect to a sphericalbearing which is attached to threaded end 16a.

The piston 10a is cut, bored and threaded as previously described toprovide a bore 20a, with threads 22a, and a chamfer 24a at one end tomate with the chamfer 36a of the new shaft 30a. The remaining steps ofthe repair method are the same as that described hereinabove.

Piston and shaft assemblies repaired by the method of the presentinvention have been tested on a 1,000 klbs. tension test machine. Thistesting method applies tensile loads similar to train action draft loadswhich the repaired devices would experience in use. The graphic resultsof two of these tests are illustrated in FIGS. 10 and 11. FIG. 10illustrates the test results for the type of repaired piston-shaftassembly illustrated in FIG. 6. FIG. 11 illustrates the test results forthe type of repaired piston-shaft assembly illustrated in FIGS. 8 and 9.In both of the tested combinations, a thread lock adhesive had beenused. In both FIGS. 10 and 11, the vertical axis represents tension, inklbs. (1,000 lbs.), and the horizontal axis represents elongation, ininches. The jagged ascending lines 50 in both graphs were due tosensitivity of the test equipment rather than yielding of the repairedpiston-shaft assembly.

In both of the illustrated tests, the repaired piston-shaft assembliesbore loads of 900 klbs.(900,000 pounds-force) without failure. In FIG.10, at a 900 klb. load, the assembly was elongated by 0.86 inches. InFIG. 11, at a 900 klb. load, the assembly was elongated by 0.90 inches.The Association of American Railroads minimum failure requirement for anE-60 coupler knuckle is 600 klbs.(600,000 pounds-force). The design loadfor many cushion pocket sill stops is 350 klbs.(350,000 pounds-force).Therefore, the test data would indicate that either coupler knuckles orsill stops would fail before a repaired piston-shaft assembly wouldseparate, with the same attachment methods of those included in thistest procedure.

Although the invention has been described with respect to the twoillustrated embodiments, the invention is not limited to theseembodiments. Additional modifications and/or additions may be includedby those skilled in the art without departing from the scope of theinvention as defined by the claims.

We claim:
 1. A method of repairing a damaged piston and shaftcombination for an end-of-car cushioning device wherein the deviceincludes a piston and a shaft connected to the piston, the methodcomprising the steps of:removing the shaft from the piston; finding thetrue center of the piston; cutting a bore through the true center of thepiston; cutting threads in the bore; cutting an angled chamfer in oneend of the bore; providing a new shaft having a central length of adiameter less than the diameter of the bore, a threaded portion at apredetermined position on the shaft, the threads having an outsidediameter greater than the diameter of the bore and being adapted to matewith the threads of the bore to provide a positive abutment againstaxial piston motion along the shaft in one axial direction, and anangled chamfer of increased diameter at one end of the threaded portion,the chamfer being adapted to mate with the chamfer of the bore toprovide a positive abutment against axial piston motion along the shaftin the other axial direction; connecting the new shaft to the old pistonby sliding the piston over the central length of the shaft and thenrotating the piston and shaft relative to each other so that thethreaded portion of the new shaft engages the threads of the bore and sothat the chamfers abut.
 2. A method as claimed in claim 1 furthercomprising the step of applying a thread lock adhesive to the threadedportion of the new shaft before connecting the new shaft to the piston.3. A method as claimed in claim 1 wherein the chamfers are angled at anangle of about 45°.
 4. A method as claimed in claim 1 wherein the newshaft is longer than the old shaft.
 5. A method as claimed in claim 1wherein the cushioning device includes a spherical bearing connected tothe old shaft and the new shaft includes a means for connecting theshaft to the spherical bearing.
 6. A method as claimed in claim 1wherein the new shaft further comprises an enlarged diameter stopintegral with and disposed adjacent the new shaft chamfer.
 7. A methodas claimed in claim 6 wherein the enlarged diameter stop is disposed onthe new shaft adjacent said threads and defines said chamfer.
 8. Amethod as claimed in claim 7 wherein said stop is disposed such thatsaid stop receives loads transferred between said piston and shaft whensaid shaft is subjected to tensile forces.